SPOJ - GSS1&&GSS3

#include<cstdio>
#include<iostream>
#define lc k<<1
#define rc k<<1|1
using namespace std;
const int M=1e5+5,N=M<<2;
struct sgt{
    int sum,gss,lgss,rgss;
}tr[N];
int n,m,a[N];
void updata(int k){
    tr[k].sum=tr[lc].sum+tr[rc].sum;
    tr[k].lgss=max(tr[lc].lgss,tr[lc].sum+tr[rc].lgss);
    tr[k].rgss=max(tr[rc].rgss,tr[rc].sum+tr[lc].rgss);
    tr[k].gss=max(max(tr[lc].gss,tr[rc].gss),tr[lc].rgss+tr[rc].lgss);
}
void build(int k,int l,int r){
    if(l==r){
        tr[k].sum=tr[k].gss=tr[k].lgss=tr[k].rgss=a[l];
        return ;
    }
    int mid=l+r>>1;
    build(lc,l,mid);
    build(rc,mid+1,r);
    updata(k);
}
sgt query(int k,int l,int r,int x,int y){
    if(l==x&&r==y) return tr[k];
    int mid=l+r>>1;
    if(y<=mid) return query(lc,l,mid,x,y);
    else if(x>mid) return query(rc,mid+1,r,x,y);
    else{
        sgt left,right,result;
        left=query(lc,l,mid,x,mid);
        right=query(rc,mid+1,r,mid+1,y);
        result.sum=left.sum+right.sum;
        result.lgss=max(left.lgss,left.sum+right.lgss);
        result.rgss=max(right.rgss,right.sum+left.rgss);
        result.gss=max(max(left.gss,right.gss),left.rgss+right.lgss);
        return result;
    } 
}
int main(){
    scanf("%d",&n);
    for(int i=1;i<=n;i++){
        scanf("%d",&a[i]);
    }
    build(1,1,n);
    scanf("%d",&m);
    for(int i=1,x,y;i<=m;i++){
        scanf("%d%d",&x,&y);
        printf("%d\n",query(1,1,n,x,y).gss);
    }
    return 0;
}

#include<cstdio>
#include<iostream>
#define lc k<<1
#define rc k<<1|1
using namespace std;
const int M=1e5+5,N=M<<2;
struct sgtment{
    int sum,gss,lgss,rgss;
}tr[N];
int n,m,a[N];
void updata(int k){
    tr[k].sum=tr[lc].sum+tr[rc].sum;
    tr[k].lgss=max(tr[lc].lgss,tr[lc].sum+tr[rc].lgss);
    tr[k].rgss=max(tr[rc].rgss,tr[rc].sum+tr[lc].rgss);
    tr[k].gss=max(max(tr[lc].gss,tr[rc].gss),tr[lc].rgss+tr[rc].lgss);
}
void build(int k,int l,int r){
    if(l==r){
        tr[k].sum=tr[k].gss=tr[k].lgss=tr[k].rgss=a[l];
        return ;
    }
    int mid=l+r>>1;
    build(lc,l,mid);
    build(rc,mid+1,r);
    updata(k);
}
void change(int k,int l,int r,int pos,int val){
    if(l==r){
        tr[k].sum=tr[k].gss=tr[k].lgss=tr[k].rgss=val;
        return ;
    }
    int mid=l+r>>1;
    if(pos<=mid) change(lc,l,mid,pos,val);
    else change(rc,mid+1,r,pos,val);
    updata(k);
}
sgtment query(int k,int l,int r,int x,int y){
    if(l==x&&r==y) return tr[k];
    int mid=l+r>>1;
    if(y<=mid) return query(lc,l,mid,x,y);
    else if(x>mid) return query(rc,mid+1,r,x,y);
    else{
        sgtment left,right,result;
        left=query(lc,l,mid,x,mid);
        right=query(rc,mid+1,r,mid+1,y);
        result.sum=left.sum+right.sum;
        result.lgss=max(left.lgss,left.sum+right.lgss);
        result.rgss=max(right.rgss,right.sum+left.rgss);
        result.gss=max(max(left.gss,right.gss),left.rgss+right.lgss);
        return result;
    } 
}
int main(){
    scanf("%d",&n);
    for(int i=1;i<=n;i++){
        scanf("%d",&a[i]);
    }
    build(1,1,n);
    scanf("%d",&m);
    for(int i=1,opt,x,y;i<=m;i++){
        scanf("%d%d%d",&opt,&x,&y);
        if(opt) printf("%d\n",query(1,1,n,x,y).gss);
        else change(1,1,n,x,y);
    }
    return 0;
}